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UA CH 102 - Exam 2 Study Guide
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moles of particles in solutionmoles of formula units dissolvedi =CH 102 1st EditionExam # 2 Study Guide Lectures: 8 – 12****EXAM ONLY ON KINETICS (Review)Van’t Hoff Factors:• Ionic compounds produce multiple solute particles for each formula unit.• The theoretical van’t Hoff factor, i, is the ratio of moles of solute particles to moles of formula units dissolved.• The measured van’t Hoff factors are generally less than the theoretical values as a result of ion pairing in solution.Therefore, the measured van’t Hoff factors often cause ΔT to be lower than you might expect.Colligative Properties of Solutions:• The colligative properties of solution depend on the number of particles dissolved, not on their identityatoms, molecules, or ions• For non-electrolytes, the Van’t Hoff factor is 1• For electrolytes, which dissociate into cations and ions in solution, the Van’t Hoff factor is greater than 1For example• NaCl (s) → Na+ (aq) + Cl- (aq) i = 2• CaCl2 (s) → Ca2+ (aq) + 2 Cl- (aq) i = 3Chemical Kinetics:– rates of chemical reactionsKinetic Molecular Theory• In order for a chemical reaction to occur the chemical species (atoms, ions or molecules)must collide• The collision must be of the correct geometry and sufficient energy• In order to increase the rate of a chemical reaction, increase the collision rate increase the concentration of reactants and increase the temperature.The rate law: An equation expressing the dependence of the rate on concentration of reactants- Zero Order: Rate = k[A]n• If a reaction is zero order, the rate of the reaction does not change. Doubling [A] will have no effect on the reaction rate.Rate law:– Rate = k[A]0 = k• Rate constant (k) units:– Rate = M/sec, k = M/sec (M sec–1)- First Order: Rate = k[A]n- If a reaction is first order, the rate is directly proportional to the reactant concentration.- Doubling [A] will double the rate of the reaction.- Rate law:– Rate = k[A]1 = k[A]- Rate constant (k) units:– When Rate = M/sec, k = sec–1Second Order: Rate = k[A]n• If a reaction is second order, the rate is directly proportional to the square of the reactant concentration.Doubling [A] will quadruple the rate of the reaction.Rate law:– Rate = k[A]2 • Rate constant (k):When Rate = M/sec, k = M−1 · sec−1Summarizing Temperature and Reaction Rate:• The frequency factor is the number of times that the reactants approach the activation barrier per unit time.• The exponential factor is the fraction of the approaches that are successful in surmounting the activation barrier and forming products.• The exponential factor increases with increasing temperature but decreases with increasing activation energy.Interpretation of the Rate Law:• describes the concentration dependence of the reaction rate• gives insight into the mechanism of a chemical reactionIn a chemical reaction bonds are broken and new bonds are formedThe reaction rate is limited by the slowest step in the reaction sequenceA reaction coordinate diagram describes the mechanism of a reaction(Practice)Reaction of Hydroxide Ion with ChloromethaneCH3Cl + OH- → CH3OH + Cl-Write the rate law for this reactionANS: Rate = k[CH3Cl][OH-]What is the value of the rate constant?ANS: 0.00049Catalysts:• Catalysts are substances that affect the speed of a reaction without being consumed. • Catalysts change the mechanism of a reaction, thereby providing a reaction pathway that has a lower activation energy• Most catalysts are used to speed up a reaction. – Catalysts used to slow a reaction are called inhibitors.• Homogeneous catalysts: all species present in same phase• Heterogeneous catalysts: species present in different phaseCatalytic Hydrogenation Reaction: CH2=CH2 + H2 → CH3CH31. Adsorption: The reactants are adsorbed onto metal surfaces.2. Diffusion: The reactants diffuse on the surface until they approach each other.3. Reaction: The reactants react to form the products.4. Desorption: The products desorb from the surface into the gas phase.Why do we care about catalyzing peroxide decomposition?Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as vegetables, fruit or animals). It catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting the cell from oxidative damage by reactive oxygen species (ROS). Likewise, catalase has one of the highest turnover numbers of all enzymes; one catalase molecule can convert approximately 5 million molecules of hydrogen peroxide to water and oxygen each


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UA CH 102 - Exam 2 Study Guide

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